Pump Devices, Methods, and Systems

ABSTRACT

A membrane-based electroosmotic pump, having catalyst regions on electrodes, can pump a fluid without applying an external voltage. Chemical reactions of fluid components on the catalyst regions on the electrodes can induce an electric field that generates an electroosmotic flow through channels of the membrane. In one embodiment, a pump comprising platinum and gold electrodes can generate the flow of the fluid containing hydrogen peroxide through channels of the membrane. In another embodiment, a pump comprising gold electrodes, on which glucose oxidase and laccase are deposited, can generate the flow of the fluid containing glucose.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional patent application Ser. No. 61/355,945, filed June 2010 by the present inventors.

BACKGROUND-PRIOR ART

The following is a tabulation of some prior art that presently appears relevant:

U.S. Patents Patent Number Kind Code Issue Date Patentee 7,086,839 B2 2003 Sep. 23 Kenny et al. 7,516,759 B2 2009 Apr. 14 Paxton et al. 7,540,717 B2 2009 Jun. 2 Sheng et al.

U. S. Patent Application Publications Publication Nr. Kind Code Publ. Date Applicant 20090308752 A1 2009 Apr. 25 Evans et al. 20070068815 A1 2007 May 29 Lu et al.

Foreign Patent Documents Foreign App or Doc. Nr. Cntry Code Kind Code Pub. Dt. Patentee 2005103490 WO A1 2005 Apr. 14 Arnold et al.

Nonpatent Literature Documents

-   Paxton, W F et al., “Catalytically Induced Electrokinetics for     Motors and Micropumps,” Journal of the American Chemical Society,     2006: 128, 14881. -   Mano, N et al., “Bioelectrochemical Propulsion,” Journal of the     American Chemical Society, 2005: 127, 11574. -   Buie, C R et al., “Water Management in Proton Exchange Membrane Fuel     Cells Using Integrated Electroosmotic Pumping,” Journal of Power     Sources, 2006: 161, 191.

FIELD OF THE INVENTION

The invention relates to an electroosmotic pump, particularly powered by catalytic reactions.

BACKGROUND

An electroosmotic pump is a particular pump where a fluid flow is driven by an externally applied electric field without moving parts such as check valves, oscillating membranes, or turbines. Briefly, surface charges within a channel attract counterions which experience a force directed along the channel axis when an electric field is applied across the channel. The viscous drag between counterions and fluid in turn exerts a force on the fluid that is localized at the channel wall, leading to a plug-like flow profile. The flow rate can be accurately controlled by the externally applied voltage. The electroosmotic pump is favorable in microfluidic devices where the surface-to-volume ratios are large. However, the electroosmotic pump usually has disadvantages of low flow rates and a high voltage operation (typically hundreds of volts).

Membrane-based electroosmotic pumps have been developed to significantly reduce the operating voltage. Due to thin membranes in ranges from several microns to hundreds microns, the membrane-based electroosmotic pumps can still keep the electric field high enough to generate a fluid flow at such a low operating voltage of less than 20 volts (FIG. 1). Further, Sheng et al. improved the flow rate of membrane-based electroosmotic pump by treating membrane surfaces with chemicals. Lu et al. designed an electroosmotic pump having a nanoporous membrane to generate a high flow rate and improve energy conversion efficiency at a low operating voltage.

On the other hand, biological membranes accelerate materials exchange across the membrane by active, ATP-dependent transport through specialized channel proteins. Similarly, the integration of “pumping” driven by chemical energy harvested from the fluid into a synthetic membrane is highly desirable from an engineering point of view, since it would obviate the need for external devices, such as power supplies, to drive flow across the membrane. Paxton et al. showed that an electric field could be catalytically induced from H₂O₂ oxidation on a Pt surface and H₂O₂ reduction on a Au surface. They found that the ions in the electric double layer near a dielectric plane between electrodes would move under the induced electric field and drag water molecules generating a fluid flow near the dielectric plane from the Pt electrode to the Au electrode. Mano et al. utilized glucose oxidation on a glucose oxidase (GOx) electrode and oxygen reduction on a bilirubin oxidase (BOD) electrode for bioelectrochemical propulsions of nanorods.

SUMMARY

A membrane-based electroosmotic pump, having catalyst regions on electrodes or catalytic electrodes, can generate a fluid flow without applying an external voltage (FIG. 2). Chemical reactions on the catalyst regions on the electrodes or the catalytic electrodes can induce an electric field that can generate an electroosmotic flow.

According to one aspect of the present invention, there is provided a pump, comprising: a membrane body, channels in the body, a first electrode and a second electrode, and fluid medium having suitable fluid components. The channels pass through the membrane body, with the first electrode mounted at one end of the channels and the second electrode mounted at the other end. The first and second electrodes are electrically connected by themselves or by an external switch. The suitable fluid component can be consumed by chemical reactions on the electrodes, generating a fluid flow through the channels of the membrane.

According to another aspect of the present invention, there is provided a pump, comprising: a membrane body, channels in the body, a first electrode and a second electrode, catalyst regions on the first electrode and the second electrode, and fluid medium having suitable fluid components. The suitable fluid component can be consumed by chemical reactions on the catalyst regions of the electrodes, generating a fluid flow through the channels of the membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a typical membrane-based electroosmotic pump in prior art.

FIG. 2 is a schematic view of a pump of the present invention, where a fluid flow is driven by catalytic reactions on electrodes or catalyst regions on electroes.

FIG. 3 shows a cross-section of a membrane prepared in accordance with one embodiment, in which platinum is deposited on a first side of a polycarbonate membrane and gold is deposited on a second side of the polycarbonate membrane.

FIGS. 4A and 4B shows a top surface and a cross-section of a polycarbonate membrane of which platinum and gold are deposited on each side in accordance with the embodiment.

FIG. 5 shows an apparatus for measuring a flow rate of fluid through channels of the membrane in accordance with the embodiment.

FIG. 6A shows how to measure tracer velocities at low flow rates and high flow rates.

FIG. 7A shows flow rates and currents when an external voltage is applied to the electrodes of the pump. Flow rate and electric current as a function of external voltage in an aqueous solution. 7B shows a rescaled plot of the voltage range from −1 V to +1 V.

FIG. 8 shows typical flow rates and current in the pump prepared in accordance with the embodiment, in which gold and platinum electrodes are used for anodic and cathodic reactions and hydrogen peroxide of 0.01 wt % is used as a fuel.

FIG. 9 shows flow rate dependent on current when the external voltage is applied. In the electroosmotic flow, the measured flow rate increases linearly with increasing measured current.

FIG. 10 shows flow rate dependent on current in the pump prepared in the embodiment. Hydrogen peroxide of 0.01 wt % is used as a fuel. The measured flow rate increases linearly with increasing measured current.

FIG. 11 shows a cross-section of a glucose-based membrane in accordance with another embodiment, in which gold, carbon nanotubes (CNTs), 1-pyrenebutanoic acid, succinimidyl ester (PBSE), and glucose oxidase are deposited on a first side of a polycarbonate membrane and gold, CNTs, PBSE, and laccase are deposited on a second side of the membrane.

FIGS. 12A and 12B show side and top view of an apparatus for measuring a flow rate of fluid through the glucose-based pump in accordance with the embodiment.

FIG. 13 shows flow rates in the pump prepared in accordance with the embodiment, in which glucose oxidase/CNTs/PBSE/gold and laccase/CNTs/PBSE/gold electrodes are used for anodic and cathodic reactions and glucose is used as a fluid component for fuel.

DRAWINGS-REFERENCE NUMERALS

-   10 electrode -   20 membrane body -   30 open chambers -   40 externally applied voltage -   50 first electrode -   60 second electrode -   70 channels of the membrane -   80 fluid medium containing fluid components -   90 electrical connection between electrodes -   100 platinum electrode -   110 gold electrode -   120 tracers -   130 narrow channel for observing tracers -   140 objective of microscope -   150 carbon nanotubes (CNTs) -   160 1-pyrenebutanoic acid, succinimidyl ester (PBSE) -   170 glucose oxidase (GOx) -   180 laccase -   190 glucose oxidase electrode (GOx/CNTs/PBSE/gold) -   200 laccase electrode (laccase/CNTs/PBSE/gold) -   210 inside chamber -   220 surrounding chamber -   230 observing channels in a chamber layer

DETAILED DESCRIPTION-ONE EMBODIMENT Hydrogen Peroxide-Based Pump

According to one embodiment of the present invention, there is provided a membrane-based pump integrating an electroosmotic pump with a fuel cell. Fuel cells are constructed in a wide range of designs and for a wide range of sources of chemical energy. In the present context, compartment-less fuel cells operating in an aqueous environment are of particular interest. In compartment-less fuel cells, a differential in the ability of the two electrodes to catalyze the anodic and cathodic reaction enables the creation of an electric potential and removes the need for an ion-exchange membrane. Among various compartment-less fuel cells, a hydrogen peroxide-based fuel cell is applied in this embodiment. Electrodes deposited on the opposing surface of a membrane generate a transmembrane potential from the hydrolysis of hydrogen peroxide in aqueous solution.

On the platinum electrode, hydrogen peroxide decomposes into oxygen, protons, and electrons. The generated electrons flow along the electrical connection, while the generated protons flow through the pores of the membrane under the catalytically induced electric field. Those electrons and protons are consumed on the gold electrode by combining with hydrogen peroxide to produce water.

To construct the hydrogen peroxide-based pump, platinum and gold were sputter-deposited on the opposing surfaces of track-etched polycarbonate membranes with a channel diameter of one micrometer (FIG. 3). A titanium adhesion layer of 5 nm and platinum and gold films of 25 nm were deposited on the opposing surfaces of a polycarbonate membrane (FIG. 4, pore diameter of 0.96 μm, porosity of 12% and thickness of 18 μm determined from analysis of SEM images) with a multi-target sputtering system. The membrane was glued to a polycarbonate frame. The platinum 100 and gold electrodes 110 were connected to metal wires using silver paste. The resistance between the electrodes after manufacturing was measured to be 0.2 MΩ. The platinum electrode and the gold electrode are electrically connected by an external switch 90.

The membrane is then integrated into a fluid chamber designed to facilitate the measurement of nL s⁻¹ pumping speeds at near-zero backing pressure (FIG. 5). A narrow channel 130 (51 μm high, 320 μm wide, 6 mm long) between two open chambers 80 was patterned with polydimethylsiloxane using a mold. The prepared chamber-channel layer and the membrane layer were assembled on glass to form an experimental set-up as shown in FIG. 5.

Flow rates were measured by microparticle image velocimetry using fluorescent microspheres 120 (1 μm diameter) as tracers. For the electroosmotic pump, the working fluid was DI water with yellow-green fluorescent microspheres (1 μm diameter, 0.002% solid loading). For the hydrogen peroxide-based pump, the fluid medium 80 was 0.01 wt % H₂O₂ solution (in DI water) with yellow-green fluorescent microspheres.

The narrow channel between the two open chambers was imaged with an Eclipse TE200U epi-fluorescence microscope equipped with an X-cite 120 lamp, a 10× objective, a cooled CCD camera, and a FITC filter cube. The focal plane was set to the center of the channel where moving tracers were clearly visible. At low flow rates, images were acquired at 100 ms intervals with 20 ms exposure times (FIG. 6A). Flow rates were calculated by measuring the particle displacement after 1 s. At high flow rates, images were acquired at 1 s intervals with exposure times ranging from 20 ms to 1 s (FIG. 6B). Flow rates were calculated by measuring the length of the streak generated by the moving particle and dividing by the exposure time. The current was measured with an ammeter. Each velocity data point is the average of 10 tracer particles velocities.

The proper functioning of the experimental setup was validated by providing an external voltage to the membrane submersed in a solution of water and tracer microspheres. An external voltage was applied between the electrodes with a DC regulated power. The dependence of electric current and particle velocity as a function of external voltage (FIG. 7) followed the behavior expected for the hydrolysis of water, which has a decomposition potential difference of 1.23 V. Positive numbers in flow rate and current correspond to flow/current from the gold electrode to the platinum electrode, while negative numbers signify the opposite direction. The flow rate is calculated from the measured velocities of tracers based on the relationship between maximum velocity and the flow rate in a rectangular channel. The flow rate increases linearly with increasing voltage across the membrane up to about 1.2 V. At an applied voltage of 1V the flow rate is −0.94 nL s⁻¹ and the current is −1.9 μA. For applied voltages above 1.4 V, flow rate and current increase linearly with increasing voltage with slopes of −43 nL s⁻¹ V⁻¹ and −120 μA V⁻¹, respectively. This implies a conductivity of the working fluid (water and tracer particles) of 2.0 μS cm⁻¹, which is close to the conductivity of water.

Using the Helmholtz-Smoluchowski equation to calculate the electroosmotic flow through the membrane while assuming a zeta potential of polycarbonate of −27 mV and considering the pressure-induced reverse flow caused by the resistance of the small outlet channel, the flow rate as a function of current can be calculated. While the calculation shows the observed linear dependence of flow rate on current with a slope of 3 nL A⁻¹ s⁻¹, it also shows that the high resistance of the small detection channel relative to the membrane resistance reduces the net flow through the membrane about 30-fold relative to the expected electroosmotic flow at zero pressure. In the electroosmotic pump, the observed pumping efficiency varies from 0.4 to 0.5 nL A⁻¹ s⁻¹ (FIG. 9), which is lower than the calculated 3 nL A⁻¹ s⁻¹.

Pumping in the absence of an external voltage is activated by the addition of hydrogen peroxide to the fluid medium at a concentration of 0.01 wt %. At this low concentration of hydrogen peroxide the formation of gas bubbles at the electrodes is avoided. The platinum 100 and gold electrodes 110 are connected to a switch 90 and an amperemeter. Fluid flow is dependent on the state of the switch: when the switch is closed, flow across the membrane commences from platinum to gold (FIG. 8); when the switch is open, the flow rate is near zero, initially with a small flow resulting from small initial pressure differences. In less than 30 s, the flow rate reaches 0.9 nL s⁻¹ and the current reaches 0.26 μA. When the switch is opened, the flow rate rapidly ceases. In subsequent switching cycles, the “closed switch” flow rates decreased by 20% after 270 min. This reduction could be the result of a falling hydrogen peroxide concentration due to its consumption at the electrodes or the result of clogging of the pores with tracer particles.

The observed flow direction (from platinum to gold) is consistent with the described pumping mechanism. The observed pumping efficiency of 3 nL A⁻¹ s⁻¹ matches the above calculated electroosmotic pumping efficiency (FIG. 10). This agreement supports the hypothesis that the pumping results from electroosmosis and not from the formation of gas bubbles at the electrodes. The observed current density on the order of 3 mA m⁻² at a hydrogen peroxide concentration of 0.01 wt % is in good agreement with Paxton et al.'s observation of 1 mA m⁻² at a concentration of 0.006 wt %. Using our model of the system, we can estimate a flow rate at zero opposing pressure of 25 nL s⁻¹ and a stall pressure of 1 Pa in the prepared pump; both parameters are typical for microfluidic pumps.

Flow Rate as a Function of Tracer Velocity

The fluid velocity in the narrow rectangular channel, v(x, y) is

$\begin{matrix} {{\frac{v}{v_{\max}} = {\left( {1 - {{\frac{2}{B}x}}^{1.54}} \right) \cdot \left( {1 - {{\frac{2}{H}y}}^{2}} \right)}},{{{for}\mspace{14mu} 0} \leq \frac{H}{B} \leq \frac{2}{3}}} & (1) \end{matrix}$

where v_(max) is the maximum velocity in the center of the channel and equals the measured tracer velocity, and the width, B, and the height, H, of the narrow channel are 3.2×10⁻⁴ m, 5.1×10⁻⁵ m, respectively. The flow rate through the channel, Q_(channel), is calculated from the measured tracer velocity, v_(max).

$\begin{matrix} \begin{matrix} {Q_{channel} = {v_{\max}{\int_{- \frac{H}{2}}^{\frac{H}{2}}{\int_{- \frac{B}{2}}^{\frac{B}{2}}{\left\lbrack {\left( {1 - \left( {\frac{2}{B}x} \right)^{1.54}} \right)\left( {1 - \left( {\frac{2}{H}y} \right)^{2}} \right)} \right\rbrack {x}{y}}}}}} \\ {= {4v_{\max}{\int_{0}^{\frac{H}{2}}{\int_{0}^{\frac{B}{2}}{\left\lbrack {\left( {1 - \left( {\frac{2}{B}x} \right)^{1.54}} \right)\left( {1 - \left( {\frac{2}{H}y} \right)^{2}} \right)} \right\rbrack {x}{y}}}}}} \end{matrix} & (2) \end{matrix}$

For a channel of the given dimensions, this yields:

Q _(channel)=(6.6×10⁻⁹ m²)·v _(max)   (3)

Conductivity of Working Fluid

The measured slope of 120 μA V⁻¹ for the I-V curve for electroosmotic pumping (FIG. 7) implies an ohmic resistance of 8.4 kΩ using

$\begin{matrix} {R = {\frac{1}{k}\frac{l}{pA}}} & (4) \end{matrix}$

where the length of the pores, l, is 1.8×10⁻⁵ m, the membrane area, A, is 9×10⁻⁵ m², and the porosity of the membrane, p, is 12%. We obtain a conductivity, k, of 2.0×10⁻⁴ S m⁻¹ which compares well with the conductivity of de-ionized water of 9.9×10⁻⁵ S m⁻¹.

Flow Rate as a Function of Current

The flow rate through membrane, Q_(pore), equals to the flow rate through channel, Q_(channel). The flow through the pore is composed of an electroosmotic and counter-pressure component:

Q _(channel) =Q _(pore) =Q _(electroosmotic) −Q _(conter pressure)   (5)

According to Lazar and Karger, the flow rate due to electroosmosis, Q_(electroosmotic), is

$\begin{matrix} {Q_{electroosmotic} = {{- \frac{{\pi ɛ\zeta}\; U}{4\eta \; l}}d^{2}N_{pore}}} & (6) \end{matrix}$

with ε as the permittivity and η as the viscosity of the working fluid, ζzas the zeta potential, d as the diameter and l as the length of the pore, and U as the applied voltage and N_(pore) as the number of pores. Utilizing U=IR together with (4) and pA=πd²N_(pore)/4 we obtain:

$\begin{matrix} {Q_{electroosmotic} = {{- \frac{ɛ\zeta}{\eta \; k}}I}} & (7) \end{matrix}$

Using ε=7.08×10⁻¹⁰ C V⁻¹ m⁻¹ (the permittivity of water at 20° C.), ζz=−27 mV, η=1.002×10⁻³ N m⁻² s (the viscosity of water at 20° C.), and k=2.0×10⁻⁴ S m⁻¹, we obtain:

Q _(electroosmotic)=(97 nL μA⁻¹ s⁻¹)·I   (8)

The flow rate due to counter pressure, Q_(counter pressure), is

$\begin{matrix} {Q_{{counter}\mspace{14mu} {pressure}} = {\frac{\pi}{128\eta}\frac{\Delta \; P_{pore}}{l}d^{4}N_{pore}}} & (9) \end{matrix}$

with ΔP_(pore) as the pressure differential across the membrane. Since this pressure is balanced by the pressure differential across the small channel ΔP_(channel), we can write

$\begin{matrix} {Q_{{counter}\mspace{14mu} {pressure}} = {\frac{\pi}{128\eta}\frac{\Delta \; P_{channel}}{l}d^{4}N_{pore}}} & (10) \end{matrix}$

The flow rate through a rectangular channel can be approximated by:

$\begin{matrix} {Q_{channel} = \frac{M\; \Delta \; P_{channel}{BH}^{3}}{12\eta \; L_{c}}} & (11) \end{matrix}$

with the channel length L_(c)=6 mm, the channel width B=320 μm, the channel height H=51 μm and the correction factor M given by

$\begin{matrix} {M = {{1 - {0.630\left( \frac{H}{B} \right)} + {0.052\left( \frac{H}{B} \right)^{5}}} \approx 0.9}} & (12) \end{matrix}$

Inserting (11) into (10), and the resulting expression into (5), we obtain:

$\begin{matrix} {Q_{channel} = {{- \frac{{ɛ\zeta}\; I}{\eta \; k}} - {\frac{3d^{2}{ApL}_{c}}{8{lMBH}^{3}}Q_{channel}}}} & (13) \end{matrix}$

which simplifies to:

$\begin{matrix} {Q_{channel} = {\frac{- {ɛ\zeta}}{\eta \; {k\left( {1 + \frac{3d^{2}{ApL}_{c}}{8{lMBH}^{3}}} \right)}} \cdot I}} & (14) \end{matrix}$

Using d=0.96 μm, l=18 μm, we obtain:

$\begin{matrix} {Q_{channel} = {{\frac{\left( {97\mspace{14mu} {nL}\; \mu \; A^{- 1}s^{- 1}} \right)}{\left( {1 + 33} \right)} \cdot I} = {\left( {2.9\mspace{14mu} {nL}\; \mu \; A^{- 1}s^{- 1}} \right)I}}} & (15) \end{matrix}$

Flow Rate at Zero Opposing Pressure

The flow rate in the absence of the counter pressure is equal to the flow rate due to electroosmosis calculated in (7) and (8). Given the maximum available current of 0.26 μA this translates into a maximum flow rate of 25 nL s⁻¹.

Stall Pressure at Zero Flow

The stall pressure can be calculated by equating (7) and (9) to be:

$\begin{matrix} {P_{stall} = {\frac{32l\; {ɛ\zeta}}{d^{2}{pAk}}I}} & (16) \end{matrix}$

For a current of 0.26 μA this yields a stall pressure of 1.4 Pa.

Consumption of H₂O₂ and Decreasing Flow Rate

The O₂ generation rate per electrode area, k_(O2), is:

$\begin{matrix} {k_{O_{2}} = {\frac{1}{2}\frac{I}{fAF}}} & (17) \end{matrix}$

where F is the Faraday constant, and f is the fraction of oxygen which originates from the electrochemical reaction H₂O₂→O₂+2H⁺+2 e⁻ (and not from 2H₂O₂→H₂O+O₂). Paxton et al. estimated f=40% based on their measurements of O₂ generation and current density for gold/platinum microelectrodes, which implies:

$\begin{matrix} \begin{matrix} {k_{O_{2}} = \frac{\left( {2.6 \times 10^{- 7}A} \right)}{2 \cdot 0.4 \cdot \left( {96485\; C\; {mol}^{- 1}} \right) \cdot \left( {9 \times 10^{- 5}m^{2}} \right)}} \\ {= {4 \times 10^{- 8}\mspace{14mu} {mol}\; m^{- 2}s^{- 1}}} \end{matrix} & (18) \end{matrix}$

Since 60% of the oxygen molecules require 2 hydrogen peroxide molecules to be produced and 40% of the oxygen molecules require only one hydrogen peroxide molecule, the hydrogen peroxide consumption rate is given by:

k_(H) ₂ _(O) ₂ =1.6k_(O) ₂   (19)

The fraction of the initially available hydrogen peroxide which is consumed after time t is approximately given by:

$\begin{matrix} {\frac{\left\lbrack {H_{2}O_{2}} \right\rbrack}{\left\lbrack {H_{2}O_{2}} \right\rbrack_{0}} = \frac{1.6k_{O_{2}}{At}}{c\; \rho \; V}} & (20) \end{matrix}$

where c is the hydrogen peroxide concentration (0.01 wt %), r is the density of the solution (1 g cm⁻³) and V is the volume of the solution (4.3 mL), and M is the molecular weight of hydrogen peroxide (34 g mol⁻¹). Inserting eq. (17) into eq. (20) yields:

$\begin{matrix} {\frac{\left\lbrack {H_{2}O_{2}} \right\rbrack}{\left\lbrack {H_{2}O_{2}} \right\rbrack_{0}} = {\frac{4}{5}\frac{MIt}{{fF}\; c\; \rho \; V}}} & (21) \end{matrix}$

At the end of the experiment described in FIG. 8, 270 minutes have passed, so that:

$\begin{matrix} \begin{matrix} {\frac{\left\lbrack {H_{2}O_{2}} \right\rbrack}{\left\lbrack {H_{2}O_{2}} \right\rbrack_{0}} = \frac{{4 \cdot \left( {{0.26 \cdot 10^{- 6}}A} \right) \cdot 270 \cdot 60}{s \cdot \left( {34\mspace{14mu} g\; {mol}^{- 1}} \right)}}{5 \cdot 0.4 \cdot \left( {96485\; C\; {mol}^{- 1}} \right) \cdot \left( 10^{- 4} \right) \cdot \left( {1000\mspace{14mu} g\; L^{- 1}} \right) \cdot \left( {0.0043\mspace{14mu} L} \right)}} \\ {= {0.7\%}} \end{matrix} & (22) \end{matrix}$

In contrast, the measured decrease in the flow rate and the current is about 20%. However, the fraction of oxygen originating from the electrochemical reaction may be sensitive to the experimental conditions, and only a fraction of the total hydrogen peroxide in the cell may be locally available to the membrane. This may cause us to underestimate the hydrogen peroxide depletion. Alternatives, which cannot be ruled out at this time, are a reduction in the catalytic efficiency of the membrane and partial clogging of the pores with tracer particles.

DETAILED DESCRIPTION-ANOTHER EMBODIMENT Glucose-Based Pump

According to another embodiment of the present invention, there is provided a membrane-based pump integrating an electroosmotic pump with another type of fuel cell. Among various compartment-less fuel cells, a glucose-based fuel cell is applied in this embodiment. Electrodes deposited on the opposing surface of a membrane generate a transmembrane potential from the electro-decomposition of glucose in aqueous solution.

On the glucose oxidase electrode 170, glucose decomposes into glucono-lactone, protons, and electrons. The generated electrons flow along the electrical connection, while the generated protons flow through the pores of the membrane under the catalytically induced electric field. Those electrons and protons are consumed on the lacasse electrode 180 by combining with oxygen to produce water. Carbon nanotubes (CNTs) 150 take a role in the electron transfer from enzymes to gold electrodes.1-pyrenebutanoic acid, succinimidyl ester (PBSE) 160 takes a role of a physically stable bridge between enzymes (GOx and laccase) and CNTs.

To construct the glucose-based pump, gold was deposited on the opposing surfaces of track-etched polycarbonate membranes with a pore diameter of five micrometer (FIG. 11). A titanium adhesion layer of 5 nm and platinum and gold films of 20 nm were deposited on the opposing surfaces of a polycarbonate membrane (pore diameter of 5 μm, porosity of 12% and thickness of 18 μm) with an e-beam evaporator. The membrane was attached to a patterned thin glass frame with a double-sided tape. CNTs dispersion (4 mg in 1 ml methanol) 5 μl was deposited on the both gold-coated surfaces and dried. PBSE (0.5 mg in 1 ml methanol) 50 μl was deposited on the CNTs/gold-coated surfaces and incubated for 20 min, and then rinsed with PBS (phosphate buffered saline, pH 7.4). Glucose oxidase solution (4 mg in 1 ml PBS) 50 μl was deposited on the one PBSE/CNTs/gold-coated surface and incubated for 10 min, and then rinsed with PBS. Laccase solution (from Trametes Versicolor, 4 mg in 1 ml PBS) 50 μl was deposited on the other PBSE/CNTs/gold-coated surface and incubated for 10 min, and then rinsed with PBS. The electrodes are electrically connected due to carbon nanotubes on channel walls.

The membrane layer is then integrated into a fluid chamber designed to facilitate the measurement of nL s⁻¹ pumping speeds at near-zero backing pressure (FIG. 12). Four observing channels 230 (100 μm high, 4 mm wide) between an inside chamber 210 and a surrounding chamber 220 in a chamber layer were patterned with one-sided tape in a Petri-dish as shown in FIG. 12B. The prepared chamber layer and the membrane layer were assembled to form an experimental set-up as shown in FIG. 12A.

Flow rates were measured by microparticle image velocimetry using fluorescent microspheres (1 μm diameter) as tracers. The working fluid was 500 mM glucose (in PBS) with yellow-green fluorescent microspheres.

The four observing channels were imaged with an Eclipse TE200U epi-fluorescence microscope equipped with an X-cite 120 lamp, a 10× objective, a cooled CCD camera, and a FITC filter cube. The focal plane was set to the center of the channel where moving tracers were clearly visible. Images were acquired at 1 s intervals with 20 ms exposure times. Flow rates were calculated by measuring the particle displacement after 29 s.

There was no fluid flow in a fluid medium (PBS) without a fluid component of glucose (FIG. 13). Pumping is activated by adding the fluid component of glucose into the fluid medium. The glucose oxidase 190 and laccase electrodes 200 are electrically connected by themselves through CNTs layers on walls of channels (FIG. 11). The membrane layer and the chamber layer are assembled so that the glucose oxidase electrode are located on the bottom surface of the membrane contacting the inside chamber 210, while the laccase electrode are located on top surface of the membrane contacting the surrounding chamber 220, as shown in FIG. 12A.

Fluid medium flows toward the center through the four observing channels 230 in the chamber layer. The direction of the fluid flow, from the glucose oxidase electrode to the laccase electrode, is consistent with the above described mechanism. The flow rate reaches about 2.5 nL s⁻¹ through each observing channel at a glucose concentration of 500 mM (FIG. 13).

It has been known that the currents generated from the chemical reactions in glucose fuel cells or other biofuel cells can be controlled by the concentrations of the fuels and that the currents can be enhanced by adding a mediator such as benzoquinone. The flow rate in this embodiment can be controlled by the concentration of glucose, since the flow rate is proportional to the current according to the Helmholtz-Smoluchowski equation. Thus, an autonomous pumping of fluid medium in response of the concentration of glucose is possible, which has a promising potential in biomedical applications.

CONCLUSION, RAMIFICATIONS, AND SCOPE

Accordingly the reader will see that at least one embodiment of the pump provides a simpler method that pumps a fluid without the need of external voltage operation. Especially, a glucose-based pump can be implanted in a body and operate by harvesting chemical energy from surrounding glucose-containing fluids so that it can obviate a power supply part.

While the above description contains many specificities, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of various embodiments thereof. Many other ramifications and variations are possible within the teachings of the various embodiments. For example, the membrane body can have different materials such as metal oxides, glasses, polymers, etc.; different kinds of channels such as mesh, fibrous, etc.; the channel size can be in a range from nanometer to millimeter; the catalyst region can have different catalysts such as other transition metals, enzymes, etc.; the fluid component for powering the pump can have different chemicals such as hydrazine, ATP, GTP, methanol, ethanol, etc.

Thus the scope should be determined by the appended claims and their legal equivalents, and not by the examples given. 

1. A method of pumping a fluid, comprising: providing a membrane body having a first side and a second side; providing channels passing through the membrane body from the first side to the second side; providing a first electrode attached on the first side and a second electrode attached on the second side; providing an electrical connection between the electrodes; providing a fluid medium, the fluid medium having a fluid component that provides chemical reactions, the chemical reactions being catalyzed by the electrodes; exposing the membrane to the fluid medium, so that the electrodes are exposed to the fluid medium, wherein the chemical reactions on the electrodes induce a flow of the fluid medium through the channels of the membrane.
 2. The method of the claim 1, wherein the membrane is selected from the group consisting of polymers including polycarbonate and metal oxides including aluminum oxide.
 3. The method of the claim 1, wherein the electrodes are metals generating a potential difference between the electrodes by being exposed to the fluid component.
 4. The method of the claim 3, wherein the metals are selected from the group consisting of gold, platinum, and copper, nickel and other transition metals.
 5. The method of the claim 1, wherein the electrical connection between the electrodes contains an external switch, so that the flow of the fluid medium through the channels of the membrane can be controlled.
 6. The method of the claim 1, wherein the electrodes are internally connected, so that the autonomous flow of the fluid medium through the channels of the membrane is possible.
 7. The method of the claim 1, wherein the fluid medium is selected from the group consisting of hydrogen peroxide and hydrazine.
 8. A method of pumping a fluid, comprising: providing a membrane body having a first side and a second side; providing channels passing through the membrane body from the first side to the second side; providing a first electrode attached on the first side and a second electrode attached on the second side; providing an electrical connection between the electrodes; providing catalyst regions on the electrodes; providing a fluid medium, the fluid medium having a fluid component that provides chemical reactions, the chemical reactions being catalyzed by the catalyst regions on the electrodes; exposing the membrane to the fluid medium, so that the catalyst regions are exposed to the fluid medium, wherein the chemical reactions induce a flow of the fluid medium through the channels of the membrane.
 9. The method of the claim 8, wherein the membrane body is selected from the group consisting of polymers including polycarbonate and metal oxides including aluminum oxide.
 10. The method of the claim 8, wherein the catalyst regions contain enzymes for oxidation and reduction of the fluid medium.
 11. The method of the claim 10, wherein the enzymes are selected from the group consisting of glucose oxidase, glucose dehydrogenases, alcohol dehydrogenases, laccase, bilirubin oxidase, and ascorbate oxidase.
 12. The method of the claim 10, wherein an electron transferer is used to help an electron flow between the enzymes and the electrodes.
 13. The method of the claim 12, wherein the electron transferer is carbon nanotubes.
 14. The method of the claim 13, wherein chemicals to create a physically stable bridge between enzymes and carbon nanotubes are used.
 15. The method of the claim 14, wherein the bridge chemicals is 1-pyrenebutanoic acid, succinimidyl ester (PBSE).
 16. The method of the claim 8, wherein the electrical connection between the electrodes contains an external switch, so that the flow of the fluid medium through the channels of the membrane can be controlled.
 17. The method of the claim 8, wherein the electrodes are internally connected, so that the autonomous flow of the fluid medium through the channels of the membrane is possible.
 18. The method of the claim 8, wherein the fluid component is selected from the group consisting glucose, oxygen, ATP, GTP, methanol, and ethanol.
 19. The method of the claim 8, wherein a mediator is added to the fluid medium to enhance the electron transfer from the enzymes to the electrodes.
 20. The method of the claim 19, wherein the mediator is benzoquinone. 